> On Oct 18, 2017, at 6:05 PM, Thibault Wittemberg via swift-dev > <swift-dev@swift.org> wrote: > > Hi everyone, > > I am a member of the RxSwiftCommunity, and I am facing an issue on a PR that > I've made (https://github.com/RxSwiftCommunity/NSObject-Rx/pull/49 > <https://github.com/RxSwiftCommunity/NSObject-Rx/pull/49>). > > The big picture is: > I have a protocol that declares a computed var (get set) with a default > implementation that uses the "objc_setAssociatedObject(self, > &disposeBagContext, disposeObject, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)" > primitive to store and retrieve its value. > Here is the complete code: > public protocol HasDisposeBag { > /// a unique RxSwift DisposeBag instance > var disposeBag: DisposeBag { get set } > } > extension HasDisposeBag { > func synchronizedBag<T>( _ action: () -> T) -> T { > objc_sync_enter(self) > let result = action() > objc_sync_exit(self) > return result > } > public var disposeBag: DisposeBag { > get { > return synchronizedBag { > if let disposeObject = objc_getAssociatedObject(self, > &disposeBagContext) as? DisposeBag { > return disposeObject > } > let disposeObject = DisposeBag() > objc_setAssociatedObject(self, &disposeBagContext, > disposeObject, .OBJC_ASSOCIATION_RETAIN_NONATOMIC) > return disposeObject > } > } > set { > synchronizedBag { > objc_setAssociatedObject(self, &disposeBagContext, newValue, > .OBJC_ASSOCIATION_RETAIN_NONATOMIC) > } > } > } > } > > The question is: what happens when it is a struct that conforms to this > protocol ?
Nothing good. It is unsafe to use objc_setAssociatedObject() with a Swift struct. For that matter you can't use objc_sync_enter/exit either. -- Greg Parker gpar...@apple.com Runtime Wrangler
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